deno test --jobs flag should require equals when passing a value

[nayeemrmn]

The --jobs flag optionally doesn't take a number value to default to the number of available cpus. So it should require an equal sign. Currently deno test --jobs tests/ doesn't work because tests/ is parsed as the number of threads. Unfortunately this is a breaking change, so this was a bad oversight.

[hyperliskdev]

I think I'd like to try and work on this.

[dsherret]

When fixing this (aka, doing this breaking change) we should consider whether we should just deprecate it in favour of the DENO_JOBS env variable. See discussion in #14929 (comment)

[nayeemrmn]

Note that we also wanted some binary flag to activate DENO_JOBS so that the test runner remained single-threaded by default. Other than retracting that expectation, a sound option would be to still deprecate --jobs and replace it with --parallel which does the same thing. It's a slightly better name for a binary flag and wouldn't have this bug.

[dsherret]

I think replacing it with --parallel makes sense given that fixing --jobs is a breaking change and it's not a great name. Also, "parallel": true in the configuration file might be a nice option in the future.